To learn how afferent discharges that originate from anterior tongue, posterior oropharynx and visceral organs interact in eliciting responses from central nervous system neurons during development, neurophysiologial responses will be recorded in the nucleus of the solitary tract (NST) and parabrachial nuclei (PBN) in rats aged four days postnatal through adulthood. When recording in the NST and PBN, taste receptors located on the anterior tongue and posterior oropharynx will be chemically stimulated with salts, hydrochloric acid, sucrose and quinine; the cervical vagus nerve, which transmits information from abdominal organs to the brain, will be electrically stimulated. The NST and PBN are first- and second-order relays in the gustatory pathway, respectively, and each has been implicated in adults as having unique functional importance for taste and ingestive behaviors. The proposed studies will provide new information on: 1) how and when taste response characteristics change at each synaptic level throughout the rat's development when anterior tongue and posterior oropharynx are stimulated independently and simultaneously, 2) how and when vagal stimulation is received by chemosensitive neurons in the NST and PBN and the influence of vagal stimulation on taste responses, and 3) how responses differ between the NST and PBN for each age. Findings may then be compared with existing knowledge of the development of taste preferences and aversions and the development of feeding to clarify the contribution of each nucleus to these behaviors. Comparisons of developmental changes between the NST and PBN may enable identification of "critical periods" for taste and for the interaction of taste with feeding which will aid in understanding the origin and mechanisms os sweet and salt preferences. Thus, these results provide new information on the development of central nervous system taste responses that relate to the development of taste preferences and aversions, and to the development of feeding and drinking.